Change URL subdirectory and filename for 437 file requests

I have 437 URL requests which were static files on Movable Type, which can only be viewed on WordPress and in a different subfolder, with modified filenames. I have tried for days to make Rewrite and Redirect work, but no success.

Here is an example in my root .htaccess file of what I need to do (this didn't work, though).

RewriteRule

http://voidnow.org/archives/2012/08/divided-america.php 

to

http://voidnow.org/WP-Void/2012/08/divided_america/

There are 4 changes to make:

• subdirectory /archives/ changed to /WP-Void/

• file-name-with-hyphens changed to file_name_with_underscores

• .php lopped off filename

• slash added to end of line

I have the following lines at the top of my root .htaccess :

Options -Indexes +FollowSymLinks
<IfModule mod_rewrite.c>
    RewriteEngine on

Please note that .php files no longer exist in the archives subdirectory. Not sure if that makes a difference, but, error logs for the failed rewrites begin by stating that the requested file is not found in the /archives/ subdirectory.